Pneumatic radial tire with helical belt layer

ABSTRACT

A pneumatic radial tire ( 20 ) comprises a radial carcass ( 22 ) of at least one ply, and a reinforcing belt ( 23 ) arranged on the outer peripheral side of the radial carcass ( 22 ). The reinforcing belt ( 23 ) is in the form of a helical belt layer ( 24 ) wherein a ribbon ( 40 ), which is comprised of a rubber ( 41 ) and a plurality of reinforcing cords ( 42 ) embedded in the rubber ( 41 ), is successively wound in a helical manner at an angle with respect to the circumferential direction of a tread portion. The ribbon (40) forming the helical belt layer ( 24 ) has a cross-section in which the reinforcing cords ( 42 ) are dispersed in the thickness and width directions of the ribbon ( 40 ).

FIELD OF THE INVENTION

The present invention relates to a pneumatic radial tire; in particular,it pertains to a pneumatic radial tire which is capable of suppressingirregular wear of the tread by an improved helical belt that is arrangedon the outer peripheral side of the carcass.

BACKGROUND ART

The tread patterns of pneumatic radial tires are often determined mainlyin view of the desired performance of the tire, such as maneuveringstability and wet performance. Also, it is conventional practice thatthe tread is formed with a plurality of grooves extending in thecircumferential direction and widthwise direction of the tire, tothereby define discrete land portions in the form of blocks. In thisinstance, there is a tendency that the tread undergoes irregular wear.One may then consider that the block configuration can be modified forthe purpose of preventing irregular wear of the tread, though suchmodifications are not practically carried out. This is becausemodification of the block configuration makes it difficult to preservethe maneuvering stability, wet performance and the like, which arerequired as the basic performance of the tire. Accordingly, it would bedesirable to suppress irregular wear of the tread by improving the beltstructure.

SUMMARY OF THE INVENTION

The present invention is based on recognition obtained with respect topneumatic radial tires in which there is arranged, on outer peripheralside of a radial carcass, a winding layer or so-called helical beltlayer wherein a ribbon comprised of a plurality of cords embedded in arubber is successively wound in helical manner with a predeterminedangle relative to the circumferential direction of the tread portion. Inconnection with such pneumatic tires, it has been conceived that thehelical belt can be improved so as to effectively suppress irregularwear of the tread without modification of the block configuration.

The inventor thus conducted through investigations on the mechanism ofoccurrence of irregular wear of the tread portion, as well ascountermeasures for suppressing and preventing the same. The result ofsuch investigations can be summarized as follows.

First of all, it is considered that irregular wear of a tire treadportion due to the driving force occurs under the following causalrelationship. That is, as illustrated in FIG. 1, attention is directedto the relative positional relationship between an arbitrary point P onthe outermost layer 11 of a tire 10, i.e., a helical belt layer, and apoint Q on the tread region which is intersected by a normal line of theoutermost belt layer passing through the point P. In this case, when thetire 10 is applied with a driving force, the tread rubber 12 undergoes ashearing deformation within the ground contact surface so that a pointQ₁ on the tread region, which is located on the normal line passingthrough a point P₁ on the belt layer 11 outside the ground contactsurface, is shifted to a retracted point Q₂ in the ground contactsurface, which is retraced rearwards of a point P₂ in the rotationaldirection R. That is the relationship indicated by the line segmentP₁-Q₁, which is perpendicular to the belt layer 11 outside the groundcontact surface, changes to the relationship indicated by the linesegment P₂-Q₂, which is inclined relative to a normal line nintersecting the point P₂ on the belt layer 11 within the ground contactsurface, during which the tread rubber 12 undergoes a shearingdeformation. This relationship is maintained until immediately beforethe tread region comes out of the ground contact surface as shown by aline segment P₃-Q₃. Then, as soon as the tread region comes out of theground contact surface, the tread rubber 12 is restored to the originalstate so that the relationship indicated by a line segment P₄-Q₄ isrecovered wherein the point Q₄ on the tread region is located on thenormal line intersecting the point P₄ on the belt layer 11 as is thecase with the point Q₁, for the line segment P₁-Q₁. This recovery causesthe shear strain of the tread rubber 12 to be rapidly released, therebycausing a sliding movement of the tread rubber 12 and a resultantincrease in the wear amount of the edge portion, particularly at thekick-out side of the block. This is a main factor of so-called“heel-and-toe wear”.

It can be therefore understood that, by reducing the shear strain of thetread rubber, which is caused immediately before the tread region comesout of the ground contact surface, it is possible to suppress theheal-and-toe wear. The inventor has experimentally confirmed that thedeformation of the tread rubber caused immediately after the treadregion steps into the ground contact surface does not significantlydepend on the belt structure of the tire. Based on such recognition, theinventor found that the wear of the tread rubber can be suppressed byreducing the relative displacement between the outermost belt layer 11and the tread, so that the shear strain indicated by the line segmentP₃-Q₃ in FIG. 1 at the kick-out side of the tread region is reduced tothe deformation which is indicated by the line segment P_(3A)-Q_(3A) inFIG. 2.

Furthermore, the inventor noted that the tread portion undergoes amarked bending deformation in the vicinity of a portion which is appliedwith the load when the tire is pressed against the road surface, and thebending deformation causes a compressive deformation along acircumferential direction of the belt layer with a longitudinal centerline of the tread portion as the center. The inventor then consideredthat, by arranging the outermost belt layer at a location spaced fromthe bending-neutral plane by as increased distance as possible, it wouldbe possible to reduce the compressive deformation amount of the beltlayer and thereby reduce the relative displacement between the outermostbelt layer and the tread. Thus, in order to have the outermost beltlayer arranged at a location spaced from the bending-neutral plane by asincreased distance as possible, a trial has been conducted in which arubber layer of approximately 1 mm in thickness was arranged between theoutermost belt layer and the second belt layer as seen from the outerside, though an intended function could not have been achieved.

Investigations were further conducted with respect to the cause thereof,and it has been revealed that the compressive deformation of theoutermost belt layer due to the bending deformation of the tread portionis absorbed by the deformation (so-called buffer deformation) of thebelt layer arranged inside of the outermost belt layer, so that theoutermost belt layer does not sufficiently undergo a compressivedeformation. Thus, in order to suppress such buffer deformation of therubber and arrange the outermost belt layer at a location spaced fromthe bending neutral plane by as increased distance as possible, a trialhas been made in which a helical layer was formed by successivelywinding, helically in the axial direction of the tire, a ribboncomprised of a rubber layer of about 2 mm in thickness, for example, andcords which are dispersed within the rubber layer not only in the widthdirection thereof but also in the radial direction of the tire, in themanner to be more fully described below with reference to illustratedembodiments. As a result, it became possible to achieve a largecompressive deformation of the outermost belt layer as indicated byoutlined arrows in FIG. 2, and increase the compressive deformationamount by approximately 25% particularly in a region adjacent to thecenter of the ground contact surface. This is because the rubbermaterial of the outermost belt layer is substantially divided by thecords and such arrangement of the cords contributes to suppression ofthe buffer deformation. Moreover, it has been found that, by suitablysetting the distance between the peak and the bottom of thecord-arrangement, due to the dispersion of cords in the radial directionof the tire, there is no problem relating to the irregularity in thewidth direction, and advantageous functions are achieved insubstantially the same manner as a single thick protection layer.

The present invention has been accomplished through the above-mentioneddevelopment process, and provides a pneumatic radial tire whichcomprises a radial carcass of at least one ply, and a reinforcing beltarranged on an outer peripheral side of the radial carcass, wherein thereinforcing belt has a helical belt layer in which a ribbon comprised ofa rubber and a plurality of reinforcing cords embedded in the rubber issuccessively wound in helical manner, at an angle with respect to acircumferential direction of a tread portion, and wherein the ribbonforms the helical belt layer having a cross-section in which thereinforcing cords are dispersed in a thickness direction and a widthdirection of the ribbon.

In carrying out the present invention, it is preferred that a curveconnecting both centers of the reinforcing cords, which are situatedadjacent to each other in the width direction in the cross-section ofthe ribbon, has at least one peak and/or bottom as seen in the thicknessdirection of the ribbon. In this instance, the curve connecting thecenters of the reinforcing cords preferably has at least one peak and atleast one bottom, so that the cords are more effectively dispersed.

In order to effectively disperse the cord, it is preferred that themaximum dispersion of the reinforcing cords with respect to thethickness direction of the ribbon, i.e., the maximum distance betweenthe highest peak and the lowest bottom in the radial direction of thetire, is set to be approximately 1 to 3 mm. Incidentally, the reason whythe dispersion in the thickness direction of the ribbon is set to bewithin a range of approximately 1 to 3 mm is that a sufficient effect ofthe dispersion cannot be achieved in the case of less than approximately1 mm, whereas the cords are excessively dispersed in the case of morethan approximately 3 mm, thereby lowering the hoop effect and degradingthe maneuvering stability.

Furthermore, it is preferred that a ratio of a widthwise center distancebetween the peak and bottom of the curve, which are adjacent to eachother, to the maximum dispersion of the reinforcing cords in thethickness direction of the ribbon, is approximately 0.2 to 6, tooptimize the dispersion of the cords.

It is also preferred that the ribbon has a cross-sectional shape whichis in the form of a parallelogram. In this case, when the ribbon issuccessively wound in a helical manner in the axial direction of thetire, the surfaces of the side edge of neighboring turns of the ribboncan be brought in positive abutment with each other.

According to the present invention, the ribbon can be produced bycontinuously extruding a plurality of cords and a rubber through amouthpiece having an extrusion orifice of 12 mm in width and 2 mm inheight, for example, such that the cords are dispersed in the thicknessand width directions of the ribbon. In order to disperse the cords in apredetermined arrangement form, all what is required is to provide acord guide member having an opening or holes corresponding in diameterto the respective cords, on the upstream side of the mouthpiece. Theribbon thus obtained provides such functional advantages as realizationof a desired arrangement of the cords at a high degree of freedom,improvement in adhesion between the rubber and cords thereby preventingseparation, in contrast to conventional ribbon obtained by calendarrolls in order to unite a plurality of cords to a rubber sheet.

In a pneumatic radial tire according to the present invention, it ispreferred that the reinforcing cords are comprised of organic fibers. Inthis connection, since the present invention serves primarily to improvethe helical belt layer, the belt layer arranged on the radially innerside of the helical belt layer at a predetermined inclination angle withreference to the circumferential direction may be comprised of eitherorganic fiber cords or steel cords.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic explanatory view for explaining the deformation ofa tread region at the ground contact portion when a tire having aconventional helical belt is applied with a driving force;

FIG. 2 is a schematic explanatory view for explaining the deformation ofa tread region at the ground contact portion when a tire having ahelical belt according to the present invention is applied with adriving force;

FIG. 3 is a meridional-sectional view of a pneumatic radial tire towhich the present invention can be applied;

FIG. 4A is a cross-sectional view of a conventional ribbon;

FIGS. 4B to 4I are cross-sectional views showing various embodiments ofthe ribbon to be used for tires according to the invention;

FIG. 5 is a diagram showing a preferred embodiment of production linefor producing the ribbon to be used for tires according to theinvention;

FIG. 6 is a front view showing one example of the insert guide in theproduction line;

FIG. 7 is a front view showing one example of the die plate in theproduction line; and

FIG. 8 is a front view showing another example of the die plate in theproduction line.

BEST MODE FOR CARRYING OUT THE INVENTION

One preferred embodiment of the pneumatic radial tire according to theinvention will be described below with reference to the drawings.

There is shown in FIG. 3 a meridional-sectional view of a pneumaticradial tire to which the invention can be applied, having a size of225/50ZR16, for example. The tire, designated as a whole by referencenumeral 20, comprises a pair of bead cores 21 (only one of which isshown), a radial carcass 22 of at least one ply which bridges betweenthe bead cores 21, and a reinforcing belt 23 which is arranged on outerperipheral side of the radial carcass 22. The reinforcing belt 23comprises a helical belt layer 25 and a laminated belt layer 26 arrangedon radially inner side of the helical belt layer 25. The helical beltlayer 23 includes a ribbon which is comprised of a rubber and aplurality of cords embedded in the rubber, preferably organic fibercords such as nylon cords, and which is successively wound in a helicalmanner at an angle with reference to the circumferential direction ofthe tread portion 24. On the other hand, the laminated belt layer 26includes two rubber-coated steel cord layers, each of which is comprisedof a rubber and a plurality of steel cords embedded in the rubber. Thesesteel cord layers are laminated one above the other such that the cordsextend at an acute angle with reference the circumferential direction ofthe tire, in opposite directions to each other with reference to theequatorial line of the tire. Although not shown in the drawing, thetread pattern is basically block pattern.

The ribbon constituting the helical belt layer 25 is formed bycontinuously extruding a plurality of nylon cords and an unvulcanizedrubber through a mouthpiece which includes an extrusion orifice of, forexample, 12 mm in width and 2 mm in height, as will be describedhereinafter. In this case, there may be arranged 50 nylon cords of 1260d/2, per 50 mm with respect to the direction which is perpendicular tothe longitudinal direction of the cords.

As shown in FIG. 4A, the ribbon 30 constituting a conventional helicalbelt layer includes a plurality of reinforcing cords 32 coated withrubber 31 and dispersed in a straight manner in the width direction, inthe cross-section of the ribbon 30. On the other hand, according to thepresent invention, the ribbon 40 constituting the helical belt layerincludes cords 42 coated with rubber 41 and dispersed not only in thewidth direction but also in the thickness direction, in thecross-section of the ribbon 40. FIG. 4B shows Embodiment 1 in which theribbon 40 has a rectangular cross-section and the cords 42 are arrangedso as to extend upward to the right side, and FIG. 4C shows Embodiment 2in which the ribbon 40 has a cross-section in the form of parallelogramand the cords 42 are arranged in the ribbon 40 so as to extend downwardto the right side. Furthermore, FIGS. 4D to 4I show Embodiments 4 to 8in which the ribbon 40 has a cross-section in the form of parallelogramand the cords 42 are arranged in the ribbon 40 in non-linear manner. Inthese cases, as seen in the cross-section of the ribbons 40, when thecenters of the cords 42 adjacent to each other in the width directionare connected by a curve, the shape of such curve (i.e., cord pattern)may be arcuate as shown in FIG. 4D, or and alternating pattern with aplurality of peaks and bottoms as shown in FIGS. 4E to 4I. In thesedrawings, “a” designates the thickness of the ribbon, “b” the width ofthe ribbon, “c” the maximum dispersion of the cords in the thicknessdirection of the ribbon, and “d” the center distance of the peak andbottom which are adjacent to each other in the width direction of theribbon. In the above-mentioned ribbon, it is preferred that the ratiod/c of the center distance “d” between the peak and bottom adjacent toeach other in the width direction, to the maximum dispersion “c” thereinforcing cords is set to be within a range of 0.26 to 6.

In order to verify advantageous functions of the present invention,performance tests were conducted with respect to a control tire having aconventional helical belt as shown in FIG. 4A, and embodiment tiresprovided with helical belts according to the embodiments shown in FIGS.4B to 4I, respectively. Each of the test tires has the samespecification as those described with reference to FIG. 3, including ahelical belt layer comprised of a ribbon in which 50 nylon cords of 1260d/2 are arranged per 50 mm. The ribbon of the helical belt in each testtire has dimensions as shown in Table 1. Each test tire has been mountedon a rim of 7J-16 under an internal pressure of 240 kPa, and secured asa rear wheel onto a rear wheel drive type Japanese passenger car havingan engine displacement of 3000 cc. Then, the car has been subjected to arunning test of 1000 km along a comprehensive test road in a testcourse, with an increased driving force applied under anaccelerated-wear condition. The performance has been evaluated bymeasuring the wear amount at the portion which exhibited the highestwear (the toe portion of a block which exhibited a heel-and-toe wear),and comparing the running distances per 1 mm in wear amount (wearresistance). The evaluated data is represented as normalized indices inTable 1, with the running distance of the control tire per 1 mm in wearamount (wear resistance) assumed to be 100.

TABLE 1 a (mm) b (mm) c (mm) d/c wear Index Control 0.7 12 0 0 100Embodiment 1 2 12 1.8 110 Embodiment 2 2 12 1.8 110 Embodiment 3 2 121.8 3.3 115 Embodiment 4 2 12 1.8 1.7 125 Embodiment 5 2 12 1.8 1.7 125Embodiment 6 3 12 1.8 2.1 132 Embodiment 7 3.5 12 3.3 0.9 135 Embodiment8 3 12 2.8 0.4 135

It can be appreciated from Table 1 that the tires according to thepresent invention defined by the embodiments exhibit improved wearresistance as compared to the control tire. It can be also recognizedthat the embodiment tires 7, 8 are equivalent in terms of wear index,though the embodiment tire 8 exhibits a maneuvering stability which isimproved to some extent as compared to the embodiment tire 7.

As described above, the ribbon constituting the conventional helicalbelt layer (FIG. 4A) is generally produced by uniting a plurality ofcords to a rubber sheet by means of calendar rollers, whereas the ribbonconstituting the helical belt layer according to the invention (FIGS. 4Bto 4I) can be produced at a higher productivity by the process andproduction line described below.

A production line 50 is shown in FIG. 5, in which cords 52 eachsubstantially straight along its length, are supplied from a pluralityof bobbins 51 corresponding in number to the cords, and these cords 52are guided to an insulation machine 54 through a comb-like guide member53. The insulation machine 54 is detachably provided with an insertguide member 55 at its inlet and a mouthpiece 56 at its outlet, andfurther with a introduction port 57 for unvulcanized rubber at thecenter upper portion thereof. A ribbon-winding device 58 is arranged ata location on the downstream side of the insulation machine 54, fortemporarily winding a ribbon 59 which has been extruded from theinsulation machine 54.

The insulation machine 54 in the above-mentioned production line 50 maybe of such type which is not equipped with an extruding screw. This isbecause the winding speed of the ribbon 59 can be adjusted dependingupon the elasticity and adhesiveness (or tackiness) of the rubber, inorder to allow the extrusion of rubber to be adequately controlled. Theinsert guide member 55 disposed at the inlet of the insulation machine54 is formed with a plurality of holes arranged according to the desiredpattern of the cords in the ribbon 59 to be produced. For example, theinsert guide 55 shown in FIG. 6 is formed with a plurality of holes 55 ahaving substantially the same pattern as the cords 42 of the ribbon 40shown in FIG. 4 d. Moreover, while the comb-like guide member 53arranged at a location on the upstream side of the insert guide member55 aims to prevent premature wear of the insert guide member 55 due tothe friction with the cord 52, it may be omitted depending upon thepositional relationship between the bobbins 51 and the insert guidemember 55. On the other hand, the mouthpiece 56 arranged at the outletof the insulation machine 54 has an orifice 56 a of about 12 mm in widthand about 2 mm in height, for example. The orifice 56 a has across-section which is rectangular (FIG. 7) when the ribbon shown inFIG. 4 b is to be produced, and which is in the form of parallelogramwhen the ribbons shown in FIGS. 4 c to 4I are to be produced. Moreover,the ribbon extruded from the insulation machine may be directly wound ona green tire, with the winding apparatus omitted.

With the production line of the above-mentioned arrangement, a pluralityof the cords unwound from the bobbins are guided to the insulationmachine through the comb-like guide member, are arranged by the insertguide member into the same pattern as the holes thereof, and are thenpassed through the inside of the insulation machine. At the same time,unvulcanized rubber is supplied thereto through the introduction port atthe upper center of the insulation machine such that the cords arrangedinto the desired pattern are coated by unvulcanized rubber. Further, theunvulcanized rubber coating the cords is shaped into a desiredcross-section, for example, rectangular or parallelogram cross-section.The so-produced ribbon is continuously wound on the winding device. Itis a matter of course that the insert guide and the mouthpiece may bedetachably arranged at the inlet and the outlet of the insulationmachine, so as to be exchangeable depending upon the desired pattern ofthe cords the desired cross-sectional shape of the ribbon.

It will be appreciated from the foregoing detailed description that,according to the invention, the helical belt arranged on the outerperipheral side of the carcass can be improved to realize a pneumaticradial tire which is capable of effectively suppressing occurrence ofirregular wear of the tread portion, particularly when the tire isapplied with a driving force.

What is claimed is:
 1. A pneumatic radial tire comprising, a radialcarcass (22) of at least one ply, and a reinforcing belt (23) arrangedon an outer peripheral side of said radial carcass (22), saidreinforcing belt having a helical belt layer (24) in which a ribbon (40)comprised of a rubber (41) and a plurality of reinforcing cords (42)embedded in said rubber (41), each reinforcing cord (42) beingsubstantially straight along its length, is successively wound inhelical manner, at an angle with respect to a circumferential directionof a tread portion, wherein: said ribbon (40) forming said helical beltlayer (24) has a cross-section in which said reinforcing cords (42) aredispersed in a thickness direction and a width direction of the ribbon(40).
 2. A pneumatic radial tire according to claim 1, wherein a curveconnecting both centers of the reinforcing cords (42), which aresituated adjacent to each other in the width direction in thecross-section of said ribbon (40), has at least one peak and/or bottomas seen in the thickness direction of the ribbon (40).
 3. A pneumaticradial tire according to claim 1, wherein the maximum dispersion (c) ofsaid reinforcing cords (42) in the thickness direction of the ribbon(40) is approximately 1 to 3 mm.
 4. A pneumatic radial tire according toclaim 3, wherein a ratio (d/c) of a widthwise center distance (d) ofsaid peak and said bottom of said curve, which are adjacent to eachother, to said maximum dispersion (c) of the reinforcing cords (42) inthe thickness direction of the ribbon (40), is approximately 0.2 to 6.5. A pneumatic radial tire according to claim 1, wherein thecross-section of said ribbon (40) is in the form of parallelogram.
 6. Apneumatic radial tire according to claims 1, wherein said reinforcingcords (42) are organic fiber cords.
 7. A pneumatic radial tirecomprising; a radial carcass (22) of at least on ply, and a reinforcingbelt (23) arranged on an outer peripheral side of said radial carcass(22), said reinforcing belt having a helical belt layer (24) in which aribbon (40) comprised of a rubber (41) and a plurality of reinforcingcords (42) embedded in said rubber (41) is successively wound in helicalmanner, at an angle with respect to a circumferential direction of atread portion, wherein said ribbon (40) forming said helical belt layer(24) has a cross-section in which said reinforcing cords (42) aredispersed in a thickness direction and a width direction of the ribbon(40), and wherein the maximum dispersion (c) of said reinforcing cords(42) in the thickness direction of the ribbon (40) is approximately 1 to3 mm.
 8. A pneumatic radial tire according to claim 7, wherein a ratio(d/c) of a widthwise center distance (d) of said peak and said bottom ofsaid curve, which are adjacent to each other, to said maximum dispersion(c) of the reinforcing cords (42) in the thickness direction of theribbon (40), is approximately 0.2 to
 6. 9. A pneumatic radial tireaccording to claim 7, wherein the cross-section of said ribbon (40) isin the form of parallelogram.
 10. A pneumatic radial tire according toclaim 7, wherein said reinforcing cords (42) are organic fiber cords.11. A pneumatic radial tire according to claim 7, wherein a curveconnecting both centers of the reinforcing cords (42), which aresituated adjacent to each other in the width direction in thecross-section of said ribbon (40), has at least one peak and/or bottomas seen in the thickness direction of the ribbon (40).